Hydrostatic drive arrangement for vehicles with automatic adaptation of circumferential forces and wheel speeds to friction and curvature conditions

ABSTRACT

A hydrostatic drive for a vehicle having front and rear wheels with respective driving hydromotors connected to the corresponding right and left wheels, respectively. A main hydraulic pump is connected in hydraulic circuit with the hydromotors while a hydromotor flow distributor lies in circuit the hydromotors and the main pump for the distribution of a hydraulic medium therebetween to adapt the rotary speeds of the individual wheels to road curvature encountered by the vehicle. A further flow distributor is connected between the drive hydromotors of each pair of right and left wheels, and between the respective hydromotors and the corresponding hydromotor flow distributor to individually adapt circumferential force at each wheel to the respective road/wheel friction.

nited States Patent Gortnar et a1.

[72] Inventors: Franc Gortnar; Zarko Zalokar; Fedor Klun; Olga Zalokar;Velena Bulog-Gortnar, all of Ljubljana, Yugoslavia [73] Assignee:Strojna Tovarna Trbovlje, Vodenska, Tr-

bovlje, Yugoslavia [22] Filed: Feb. 27, 1970 21 Appl. No.: 15,138

[52] US. Cl [51 Int. Cl [58] Field of Search ..180/6.48, 60/53 R, 180/66R ..B62d 11/04 ..180/6.3, 6.4 B, 44 F, 66 R;

[56] References Cited UNITED STATES PATENTS 3,344,879 10/1967 Glomb eta]. ..180/66X 3,151,694 10/1964 Rogers ..180/66X [151 3,656,70 1451 Apr.18, 1972 Primary Examiner-Leo Friaglia Assistant Examiner-Leslie J.Paperner Attorney-Karl F. Ross [5 7] ABSTRACT A hydrostatic drive for avehicle having front and rear wheels with respective driving hydromotorsconnected to the corresponding right and left wheels, respectively. Amain hydraulic pump is'connected in hydraulic circuit with thehydromotors while a hydromotor flow distributor lies in circuit thehydromotors and the main pump for the distribution of a hydraulic mediumtherebetween to adapt the rotary speeds of the individual wheels to roadcurvature encountered by the vehicle. A further flow distributor isconnected between the drive hydromotors of each pair of right and leftwheels, and between the respective hydromotors and the correspondinghydromotor flow distributor to individually adapt circumferential forceat each wheel to the respective road/wheel frictron.

PATENTED R B Z 3,658,570 sum 2 OF 7 fine/r/TTUPNE) PATENTEDAPR 18 I9723, 656,570

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HYDROSTATIC DRIVE ARRANGEMENT FOR VEHICLES WITII AUTOMATIC ADAPTATION OFCIRCUMFERENTIAL FORCES AND WHEEL SPEEDS TO FRICTION AND CURVATURECONDITIONS FIELD OF THE INVENTION The subject of the invention is ahydrostatic drive arrangement for vehicles with automatic adaptation ofcircumferential forces and wheel speeds to friction and curvatureconditions, particularly for heavy automotive machines for earthworking,fitted with tire-equipped wheels.

BACKGROUND OF THE INVENTION There are known mechanical or combinationhydromechanical drives for heavy automotive machines of this kind, inwhich the problem of vehicle driving and adaptation of circumferentialforces of driving wheels to momentary friction conditions of the groundwhereupon the vehicle drives and of adaptation to driving in curves isnot solved in a satisfactory manner. The known drives mentioned abovehave the following drawbacks: the efiiciency of the hydrodynamic torqueconverter is very low in the range of high torques and low speeds of theoutput shaft, i.e. with low speeds and high thrust or traction forces,e.g. of a loader, bulldozer, scraper, or dumper. The engine power is notwell utilized in the case when it is most necessary. The consequencethereof is that a more powerful driving engine must be used than isactually required by the machine.

Mechanical differentials utilize the traction forces ofiered by thefriction between the driving wheels and the ground poorly. On buildingsites or grounds without roads there has to be taken into account thatthe driving wheels of the vehicle may stand on substrates havingdifiering friction coefficients. A shaft with a mechanical differentialcan develop only a twofold traction force of the wheel resting on asubstrate with a lower friction coefficient although the groundsupporting the other driving wheel of the vehicle affords for a greaterfriction force.

As a consequence thereof, machines with tireequipped wheels must by 50percent be heavier than caterpillar (tracked) vehicles in order torealize the same traction forces.

When driving in curves with four-wheel drive vehicles, the

wheels of vehicles or machines, respectively, equipped with a rigidchassis and one steering axle sideslide. This phenomenon is attributedto inconvenient geometry of the steering linkage which requires that thewheels of the steering axle run faster than the wheel of the rigid axle.A part of the engine power is thereby consumed for the wear of tireswhereby the already low friction coefficient between the ground and thetires low is further reduced due to sidesliding. Beside the excessivewear of tires an unfavorable consequence thereof is the need for aheavier engine than otherwise required. Sidesliding of tires, however,appears not only with machines with a rigid chassis, but also withmachines with an articulated chassis. With these machines the drawbackmentioned is due to variations of tire radii caused by non-uniform wheelloading.

Thus it must be taken into consideration that driving of scrapers ordumpers is not feasible by single-axle or two-axle tractors on wheelshaving a single engine. If the rear axle should also be driven, it mustbe provided with a complete engine drive whereby the machine becomesextraordinarily expensive.

OBJECTS OF THE INVENTION It is the aim of present invention to removethe drawbacks mentioned in the drives of heavy automotive buildingmachines. Thus the invention has as its task to provide such a drivethat has a higher efficiency in the domain of extreme circumferentialforces on the wheels than the hitherto known combinedhydrodynamical-mechanical speed or ratio changer composed of ahydrodynamic torque converter and a mechanical gear change with gearspermanently engaged and with selection of mechanical gears by diskclutches known as gear change with power shift."

Rotational speeds of individual driving wheels must be mutuallyindependently and automatically adapted to the length of their paths andto various tire radii which arise due to varying wheel loadings duringoperation.

Circumferential forces of individual driving wheels must also bemutually independent and automatically adapted to variable frictionforces which vary in dependance upon varying friction coeflicients underindividual wheels and upon their varying loadings. These objects arerealized by a hydrostatic drive arrangement for vehicles with automaticadaptation of circumferential forces and wheel speeds to friction andcurvature conditions with a common control pump and hydromotors for thedrive of individual wheels of the vehicle; this arrangement comprises ahydromotor-type flow distributor between the front and the rear axles inthe hydraulic circuit at connection points, for the distribution of thehydraulic medium supplied by a main control pump between the group ofdriving hydromotors of the front axle of the vehicle and the group ofdriving hydromotors of the rear axle of the vehicle and for adapting therotational speed of individual wheels of the vehicle to actual curvatureconditions. Furthermore, the said hydromotor-type flow distributor is onone hand connected by a pipeline to a valve-type distributor for thedistribution of the hydraulic medium between the driving hydromotors ofthe left-hand and right-hand wheels of the rear axle and for adaptationof the circumferential force of any individual wheel to actual frictionconditions, and is on the other hand connected by a pipeline to anothervalve-type distributor for the distribution of the hydraulic mediumbetween the driving hydromotors of the right-hand and left-hand wheelsof the front axle and for adaptation of the circumferential force of theindividual wheel to actual friction conditions.

DESCRIPTION OF THE DRAWING The invention will be explained in detail bysome examples, with reference to the accompanied drawing in which:

FIG. 1 is a diagram of a hydrostatic drive of individual wheels of oneaxle of the vehicle, with a parallel hydraulic connection ofhydromotors, without an automatic arrangement for the adaptation ofcircumferential forces and wheel speeds to friction and curvatureconditions;

FIG. 2 is a diagram of an arrangement of a hydrostatic drive of avehicle with automatic adaptation of circumferential forces and wheelspeeds to friction and curvature conditions with a hydromotor-type flowdistributor for the distribution of the hydraulic medium between thehydromotor groups of the front and rear axles and two flow distributorsfor the distribution of the hydraulic medium between the drivinghydromotors for the wheels .of the front and rear axles, respectively;

FIG. 3 is an axial cross-sectional view of a valve-type distributor forthe distribution of the hydraulic medium between the driving hydromotorsor groups of driving hydromotors;

FIG. 4 is a diagram of a hydromotor-type distributor for thedistribution of the hydraulic medium between the driving hydromotors orgroups of driving hydromotors;

FIG. 5 is a diagram, with parts shown is section, of a flow distributorwith feeler pumps for the distribution of the hydraulic medium betweenthe driving hydromotors or groups of driving hydromotors;

FIG. 6 is a flow circuit of a hydrostatic drive arrangement for avehicle with automatic adaptation of circumferential forces and wheelspeeds to friction and curvature conditions for driving in low gear(speed);

FIG. 7 is a flow circuit of a hydrostatic drive arrangement for avehicle with automatic adaptation of circumferential forces and wheelspeeds to friction and curvature conditions for driving in medium gear(speed); and

FIG. 8 is a flow circuit of a hydrostatic drive arrangement for avehicle with automatic adaptation of circumferential forces and wheelspeeds to friction and curvature conditions for driving in high gear(speed).

SPECIFIC DESCRIPTION FIG. 1 shows a hitherto known hydrostatic drive ofindividual wheels on one axle of the vehicle with the hydraulic parallelconnection of hydromotors without the arrangement according to theinvention for automatic adaptation of circumferential forces and wheelspeeds to friction and curvature conditions of the drive. This figureserves for a theoretical presentation of drawbacks of hitherto knownhydrostatic drives and for the explanation of theoretical principles ofthe hydrostatic drive arrangement according to the invention.

It is known that traction forces occurring beneath individual wheels ofvehicles or machines for earthworking may exceed the available frictionforces due to rapidly varying friction coefficients between variousportions of the ground and the tires. In such a case the parallelconnection of driving hydromotors of individual wheels is unsatisfactorywithout additional control devices. The driving hydromotor of a wheelwhich starts to sideslide rotates quicker than suited to its kinematicconditions. Due to quicker rotation it consumes more oil. Thereby ittakes away a part of the oil intended for the other wheel of that axle.Thus the oil pressure diminishes, and the traction force of the machineor the vehicle is reduced. In order to obtain optimum traction forcesparallel connection of hydromotors is applied, but for avoidingsidesliding of the wheels, devices must be introduced which maintain acorrect flow rate of the hydraulic oil.

With a hydrostatic drive according to FIG. 1, where each individualwheel is rigidly linked to the associated hydromotor, during the drivein a curve the following conditions are observed: If a drivinghydromotor in one revolution consumes an oil quantity q and the wheelcovers a path of 21", then for the rotation around the instantaneouscenter of rotation the axle consumes the following oil quantity(reference marks according to FIG. 1):

Q Q QN= q/21rr (R+b) q/21rr (R-b) q/1rr- R The difference of quantitiesfor the drive of an outer and an inner wheel is:

Devices realizing such a distribution of oil flow can be divided intothose distributing the oil between the driving hydromotors forcibly,such as hydromotor-type distributors which distribute the oil betweenthe groups of hydromotors of the front and rear axles, and into thosesupervising the correctness of flow, intervening only in the case whenthey detect an incorrect run of the motors due to sidesliding of wheelse.g., valve-type distributors, or distributors with feeler pumpsdistributing the oil between the hydromotors of the same axle.

The hydrostatic drive arrangement for a vehicle with an automaticadaptation of circumferential forces and wheel speeds to friction andcurvature conditions in an embodiment with a hydromotor-type distributorfor a forced distribution of the hydraulic medium between the groups ofdriving hydromotors of the two driving axles and with a valve-type flowdistributor for the distribution of the hydraulic medium between thedriving wheels of each axle is shown in FIG. 2. It comprises a maincontrol pump 1 the pressure side of which is connected to a four-waydistributor 2 and a hydromotor-type distributor 3, 4, 5 located in thehydraulic circuit at connection points 25, 26, 27 for the distributionof the entire quantity of the hydraulic medium between the group ofdriving hydromotors 20, 21 of the front axle and the group of drivinghydromotors 23, 24 of the rear axle of the vehicle. Between the circuitsconnecting one or the other side of the hydromotor-type distributor 3,4, 5 to the group of driving hydromotors 20, 21 or 23, 24 on the frontor rear axles, respectively, on the connection points 14, 15, 16 or 17,18, 19 a valve-type distributor 13 or 22 is connected for thedistribution of the hydraulic medium between the driving hydromotor 20of the right-hand wheel and the or for the distribution between thedriving hydromotor 23 of the right-hand wheel and the driving hydromotor24 of the left-hand wheel of the rear axle and for the independentadaptation of the circumferential forces of individual wheels to actualfriction conditions. The hydromotor-type distributor 3, 4, 5 comprisesauxiliary constant-flow hydromotors 3, 4 and a control pump 5 the shaftsof which are mechanically interconnected. Thereby the hydromotors 3, 4on one connection side are connected in parallel to the connection point27 of the hydraulic circuit, while on the other connection side they areindividually connected to connection points 25, 26 of the hydrauliccircuit and through the distributor 6 to the first or second pipeconnection of the control pump 5, respectively, the flow-controlmechanism which is mechanically linked to the steering mechanism of thevehicle.

In the hydraulic circuit of the hydrostatic drive between drivinghydromotors 20, 21 of the front axle and the valvetype distributor 13there are installed distributors 7, 8, 11 and 12, while distributors 9,10 are installed between the driving hydromotors 23, 24 of the rear axleand the valve-type distributor 22. By shifting into various positionssaid distributors faciliate the changing of the hydraulic drive into thelow, medium or high gears (torque ratios) of driving speed. FIG. 3 showsa detailed embodiment of the valve-type distributor 13 or 22 thearrangement of which in the hydraulic circuit is shown in FIG. 2. Thevalve-type distributor mentioned comprises a feeler assembly 28 whichdirectly reacts on differences of flow pressures caused by sideslidingof one of the wheels of the front or rear axle, respectively. The feelerassembly 28 is arranged in one part of the common casing 29 and providedwith connections 15, 16 or 18, 19, respectively, for the maindistributing pipelines for the driving hydromotors of individual wheelson the front or rear axil of the vehicle (FIG. 2) and with channels 30,31 connecting the feeler assembly to the control throttle distributor 32arranged in the second part of the common casing 29. In the middle partof the common casing where the throttle distributor is arranged, aconnection 14 or 17 is provided for a pipeline interconnecting thedistributor 13 or 22 and the hydromotor-type distributor 3, 4, 5 (FIG.2). Said distributor further comprises a control four-way distributor 33with a built-in piston servomotor 34 which through connection pipes 35,36 and 37, 38 is connected to the feeler assembly 28. The four-waydistributor 33 comprises connections 39, 40 which through pipelines 41,42 and a reversing valve 43 are connected in parallel or crosswise tothe connections 44, 45 of the control throttle distributor 32. Theconnection 46 is intended for a pipeline to a not shown control oil tankand the connection 47 for the pipeline to a not shown control-oil supplypump.

The feeler assembly 28 comprises two groups, placed closely together, ofsuccessive chambers 48, 49, 50 and 51, 52, 53 where the chambers 48, 49or 51, 52, respectively, are divided by a partition wall 54 or 55. Eachof the partition walls mentioned is fitted with a bore into whichprotrudes the cylindrical head 56 or 57, respectively, of a movableshutter 58 or 59. The stem 60 or 61 of the cylindrical head protrudesthrough chamber 50 or 53 and is on its thickened end part guided incover 62 or 63 and equipped with a pressure spring 64 or 65 supportedbetween plates 66, 67 or 68, 69 which are slidably fitted to the thinnerpart of the stem 60 or 61. In the intermediate position of thecylindrical head 56 or 57, said supporting plates rest against thepartition wall equipped with a bore between chambers 49, 50 or 52, 53and against the cover 62 or 63, while in the eccentric position theylean against the pertinent thickened part of the stem or against theneck of the cylindrical head 56 or 57 of the movable shutter. Close tothe partition wall 54 or 55 on the outer wall of chambers each one ofchambers 48, 49 or 51, 52 comprises a pipe connection 70, 71 or 72, 73for pipelines 36, 35 or 38, 37 leading into the piston servomotor 34. Onits mantle the cylindrical head 56 or 57 of the movable shutter 58 or 59comprises at least one longitudinal slot 74 or 75 the cross-section ofwhich increases driving hydromotor 21 of the left-hand wheel of thefront axle 75 continuously from a minimum value in the middle of thelength of the cylindrical head towards both ends of the head. Thesupporting plate 66 or 68 slidably mounted on the stem 60 or 61 of themovable shutter 58 or 59 comprises a bore 76 or 77 for equalization ofthe oil pressure in chambers 49, 50 or 52, 53. The chamber 80 or 81 inthe cover 62 or 63 is by a channel 78 or 79 connected to the chamber 50or 53 for pressure equalization of both chambers.

The throttle distributor 32 placed in the transverse part of the commoncasing 29 comprises a piston 82 with tapered piston parts 83, 84reaching into distribution chambers 85, 86 which are interconnected by aconnection channel 87 equipped with a supply connection 14/17 for theconnection of the pipeline for the driving hydraulic medium the positionof which in the hydraulic network of the hydrostatic drive is shown inFIG. 2. The piston 82 of the distributor has on both ends steps 88, 89of smaller diameter protruding into chambers 90 or 91 with connections44 or 45 for the control hydraulic medium the steps have slidablymounted supporting plates 92, 93 which hold one end of the helicoidalpressure spring 94 or 95 resting with its other end on the cover 96 or97.

The four-way distributor 33 with a built-in servomotor 34 comprises acontrol piston 98 with an intermediate control element (spool) 99 forthe control of flow through the intermediate chamber 103 equipped with aconnection 47 for the supply of controlling hydraulic medium andterminal control elements (spools) 100, 101. These terminal elements areintended for the control of flow through end chambers 102, 104interconnected by a transverse channel which is equipped with aconnection 46 for the pipeline of discharging into the tank. On one sideof the intermediate chamber 103, the casing 105 comprises a chamber 106with a supply channel 39 for the control pipeline 41, and on the otherside a chamber 107 with a supply channel 40 for the control pipeline 42.To one end the control piston 98 of the distributor has fitted ahelicoidal pressure spring 108 placed between the supporting plates 109,110 slidably mounted on the stem 111 where one of said plates restsagainst the terminal control element 101 and the other against thelimiter 112 whereby, in the intermediate position of the control piston98 of the distributor, said supporting plate 109 or 110 with itscircumferential part rests against the casing 105 or cover 113,respectively.

The piston-type servomotor 34, which is mounted at one lateral side ofthe four-way distributor 33, comprises pistons 114 and 115 which aremutually spaced and fixed to the piston rod 116 which on one side isarticulated to the control piston 98 of the four-way distributor, and acylinder-shaped casing 117. A partition wall 118 divides this casinginto two separate chambers whereby the piston 114 in the first chamberdivides the latter into a compartment 119 equipped with a connectionchannel 120 for the pipeline 35 and a compartment 121 equipped with aconnection channel 122 for the pipeline 36, while the piston 115 in theother chamber divides the latter into a compartment 123 equipped with aconnection channel 124 for the pipeline 38 and a compartment 125equipped with a connection channel 126 for the pipeline 37.

A second embodiment (FIG. 4) of the hydrostatic drive arrangement forvehicles with automatic adaptation of circumferential forces and wheelspeeds to friction and curvature conditions has an identical arrangementof particular assemblies as described above and shown in FIG. 2, withthe only difference that the distributor for the distribution of thedriving hydraulic medium between the driving hydromotors 20, 21 or 23,24 of the front or rear axle of the vehicle across connection points 14,15, 16 or 17, 18, 19 a hydromotor-type distributor 13 or 22' isconnected instead of valve-type distributors (FIG. 2). As obvious fromFIG. 4, a hydromotor-type distributor 13 or 22' consists of a first anda second auxiliary hydromotor 3', 4 and a control pump the shafts ofwhich are mechanically interconnected. The auxiliary hydromotors 3, 4are on one connection side connected in parallel by a pipeline toconnection points 14 or 17 of the hydraulic circuit, and on the otherconnection side each is separately connected to connection points 15 or16 and 18 or 19 of the hydraulic circuit and to the first or second pipeconnection of the control pump 5'.

A further embodiment (FIG. 5) of the hydrostatic drive arrangement forvehicles with automatic adaptation of circumferential forces and wheelspeeds to friction and curvature conditions comprises a similararrangement of assemblies as the two embodiments described and shown inFIG. 2, with the difference that for the flow distribution of thedriving hydraulic medium between the driving hydromotors 20, 21 or 23,24 of the front or rear axles, respectively, it comprises a flowdistributor 13" or 22" with feeler pumps (FIG. 5), connected toconnection points 14, 15, 16 or 17, 18, 19, whereby each individualdriving hydromotor 20 or 21 of the front axle of the vehicle ismechanically connected to the feeler pump 211 or 210, and in the sameway the individual hydromotors 23 or 24 of the rear axle aremechanically connected to pertinent feeler pumps. The embodiment of flowdistributor 13" with feeler pumps intended for the distribution of thehydraulic medium between the driving hydromotors 20, 21 of the frontaxle of the vehicle and that of the flow distributor 22" with feelerpumps are identical.

The flow distributor 13" with feeler pumps shown in FIG. 5 comprises aconstant-flow hydromotor 204 which is in the driving hydraulic circuitthrough a direction distributor 206 and a throttle distributor 207connected in parallel to one side of the driving hydromotors 20, 21 ofthe front axle of the vehicle, while their other sides are mutuallyconnected by a pipe from which a pipe 203 is branched for the connectionto the driving pump. The hydromotor shaft is mechanically linked to thecontrol pump 205 which for obtaining changes of flow is mechanicallyconnected to the steering mechanism for the wheels; the control pumpalso has and by pipelines 212, 213 inserted into the control circuitwhich by pipe branches 208, 209 connects the feeler pumps 210, 211 theshafts of which are mechanically linked to the shafts of the drivinghydromotors. The control pump 205 is, through pipelines 212, 213 andpipe branches 2141 215, connected to the direction valve 206 which hasits extreme double outlet pipe sections connected to the feed pipe 216or 217 each of which is connected to one end of the throttle valve 207.In connection pipeline sections 208, 209 for the feeler pump 210 or 211nonreturn valves 218, 219 and 220, 221 are placed blocking in thedirection towards the feeler pump.

In parallel with the non return valves mentioned throttle valves 222,223 or 224, 225 are inserted into by-pass pipelines. Pipe branches 226,227 or 228, 229, respectively, connected to connection pipeline sectionsof the feeler pump 210 or 211 are provided with nonreturn valves whichopen towards the feeler pump 210 or 211, unite behind the nonreturnvalves into a common pipeline which through a pipe cross-joint 231 or230 leads to a relief valve 233 or 232 connected by a connection pipe235 or 234 to branch 209 or 208 of the control circuit. The pipecross-joint 230 or 231 is on one side connected to the oil tank 236 or237 and on the other side through a throttle 238 or 239 to branch 208 or209 of the control circuit, whereby said branches are in their centersinterconnected by a pipeline 240 provided with the pertinent valves andconnected to a common feeder pipe 241 for the control circuit.

OPERATION FIG. 6 shows the circuit of the hydrostatic drive arrangementwith automatic adaptation of circumferential forces and wheel speeds tofriction and curvature conditions when driving in low gear. In order tofaciliate examination, in the diagram the supply pipelines are drawnwith heavy solid line, while return pipelines are drawn with a heavybroken line. In low gear where the vehicle drives with minimum speed allfour driving hydromotors 20, 21, 23, 24 are by the hydraulic circuitconnected in parallel to the main control pump 1. The pressure side ofthe main control pump 1 is connected through the four-way distributor 2by a pipeline in parallel to one side of each of the auxiliaryhydromotors 3, 4 of the hydromotor-type distributor. The shafts of thetwo auxiliary hydromotors are mechanically interconnected so that theydistribute the hydraulic medium in equal quantities to the groups of thedriving hydromotors of the front and rear axles. Also firmly connectedwith the shafts of both auxiliary hydromotors is the hydraulic controlpump 5 the control mechanism of which is mechanically connected with thesteering mechanism for the wheels. The hydraulic control pump 5 has,with the vehicle driving straight ahead, an eccentricity whereby in sucha control position the supply of the control pump equals zero. As soonas the vehicle enters a curve, the steering axle covers a longer pathand consumes more oil. In order to prevent sidesliding the oil supplyfor the group of driving hydromotors on the steering axle must beincreased. This increase of oil supply is realized by pump 5. Whendriving in a curve, the pump draws oil from the pipeline connecting thehydromotor 4 to the valve-type distributor 22 for the rear axle of thevehicle, supplying it to the pipeline connecting the hydromotor 3 andthe valve-type distributor 13 for the front axle of the vehicle in thecase the front axle is used as steering axle.

The oil flows from the hydromotor 3 to the valve-type flow distributor13 which distributes the oil between connection points 15, 16. Furtherthe oil flows from the connection point 15 through four-way distributors7 and 11 to the driving hydromotor 20 of the right-hand front wheel fromwhich it returns through the return pipeline shown by a dotted line inthe diagram and passes through the four-way distributor 11 to thesuction pipe of the common control pump 1. From the connection point 16the oil flows through the four-way distributor 12 to the drivinghydromotor 21 of the left-hand front wheel wherefrom it passes throughthe return pipeline shown by a dotted line in the diagram through thefour-way distributor 12 and through the four-way distributor 8 into thereturn pipeline connected to the suction pipe of the common control pump1.

From the hydromotor 4 the oil flows to the valve-type flow distributor22 connected to connection point 17 and distributing the oil betweenconnection points 18 and 19. Then the oil flows from the connectionpoint 18 through the fourway distributor 9 to the driving hydromotor 23of the right-hand rear wheel wherefrorn it returns by the returnpipeline through the four-way distributor 9 to the suction pipe of themain control pump 1. From the connection point 19 of the distributor 22the oil flows through the four-way distributor into the drivinghydromotor 24 of the left-hand rear wheel and it returns therefromthrough the return pipeline passing through a fourway distributor 10into the suction pipe of the main control pump 1.

FIG. 7 shows the circuit of the hydrostatic drive arrangement forvehicles according to present invention when driving in middle gear. Forthis circuit also there are in the diagram the supply pipelines shown bysolid heavy lines and the return pipelines by heavy dotted lines. Inmiddle gear only the hydromotors 20, 21 of the front axle of the vehicleare connected to the main control pump 1, and in parallel. In this gearthe distributors 2, 6, 9 and 10 are shifted to the position of themiddle gear, whereby the pressure oil flows from the main control pump 1through a four-way distributor 2 into the valve-type distributor 13which distributes the oil between the connection points 15, 16. From theconnection point oil flows through four-way distributors 7, 11 into thedriving hydromotor of the right-hand front wheel wherefrom it returnsafter having performed its operation through the fourway distributor 11into the suction pipe of the main control pump 1. From the connectionpoint 16 the oil flows through the four-way distributor 12 into thedriving hydromotor 21 wherefrom it returns after having performed itsoperation through the four-way distributors 12 and 8 into the returnpipeline connected to the suction pipe of the main control pump 1.Thereby the circuit of the driving hydromotors of the rear, not drivenaxle, is short-circuited by connecting both connection pipelines of thehydromotor 23 in the four-way distributor 9 and connecting bothconnection pipe-lines of the hydromotor 24 in the four-way distributor10. In this gear the control pump 5 appertaining to the hydromotor-typedistributor has no function as it is also short-circuited through thedistributor 6.

FIG. 8 shows the circuit of the hydrostatic drive arrangement forvehicles according to present invention when driving in high gear. Forbetter survey, pipelines of oil which had partly accomplished itsoperation are drawn in dash-dotted lines, while the return pipelines aredrawn in dot lines.

In high gear, i.e. at top speed of the vehicle, only the drivinghydromotors 20, 21 of the front axle are series connected to the maincontrol pump 1. With the circuit of FIG. 8, the two driving hydromotorsin spite of their series arrangement are not supplied by equal oilquantities because they are connected to a hydraulic differential. Thisis the reason why the vehicle renders good driving properties in curves.With the positions of distributors 2, 6, 7, 8, 11, 12, 9, 10 accordingto FIG. 8 the higher gear is thrown in, whereby oil from the maincontrol pump 1 is led through the four-way distributor 2 from the lattera major oil quantity is led through the four-way distributor 12 into thedriving hydromotor 21 of the left-hand front wheel of the vehicle whereit gives up approximately one-half of its energy and then flows at halfpressure through a pipeline which is shown in dash-dotted lines in thediagram and then through four-way distributors 12, 8, 11 into the secondseries-connected driving hydromotor 20 of the righthand wheel of thefront axle. Therefrom the main oil quantity returns through thedistributor 11 and then through the return pipeline back to the suctionside of the main control pump 1. To this basic circuit through whichflows the entire oil in the case of equal rotations of both wheels, anauxiliary circuit is connected which links the distributor 2 to theauxiliary hydromotor 3 of the hydromotor-type flow distributor. Further,a pipeline with half oil pressure is branched from the distributor 8connecting in parallel the second side of the auxiliary hydromotors 3,4, whereby the first side of the auxiliary hydromotor 4 is connected bya pipeline shown by a dot-dash line in the diagram, through thedistributor 7 to the return pipeline which connects the distributor 11to the suction side of the main control pump 1. This connection betweenthe two auxiliary hydromotors 3, 4 establishes a hydraulic differentialwhich is necessary for the series connection of the driving hydromotors20, 21 when driving in curves. For driving straight ahead the drivinghydromotors 20, 21 are equally loaded. Thereby the auxiliary hydromotors3, 4 of the hydromotor-type distributor on the side of the parallel pipeconnections drawn in dash dot lines are exposed to an equal half-valueforce tending to rotate both hydromotors in the same direction. On theopposite connecting side, the auxiliary hydromotor 3 is connected to thepressure pipeline of the main control pump 1, whereby on this side theauxiliary hydromotor 3 is exposed to the opposed full force of the fullpressure of the driving oil. In this way the resultant which tries torotate the auxiliary hydromotor 3 acts with a force of half the pressurein the direction determined by the oil flow in the supply line shown bya solid line. On the opposite side the auxiliary hydromotor 4 isconnected to the return pipeline drawn as a dotted line where thereturning oil has a pressure of approximately zero. The resultant whichtries to rotate the auxiliary hydromotor 4 thus acts with a force ofhalf the pressure in the direction determined by the oil flow in thehalf-pressure pipeline (represented by a dash-dot line). In this way theauxiliary hydromotors 3 or 4, respectively, are exposed to equal opposedforces which try to rotate the two auxiliary hydromotors in oppositedirections. For this reason the auxiliary hydromotors 3, 4 stand still,and there is no oil flow therethrough when the vehicle drives straighton.

When driving e. g. in a right-hand curve, the left-hand wheel must havea higher speed than the right-hand one. In this way the right-hand wheeland its driving hydromotor 20 are braked, while the left-hand wheel andits driving hydromotor 21 are additionally driven. The pressures inconnecting pipelines of the auxiliary hydromotor 4 change in the mannerthat a greater pressure difference acts on this hydromotor due toincreased pressure of the driving pipeline represented by a dash-dotline) which connects the auxiliary hydromotor 4 with the drivinghydromotor 20. The hydromotor 4 starts to rotate and runs the hydromotor3 which in this case operates as a pump and takes away oil from thepipeline connecting the hydromotor 3 through the distributor 8 to theconnection line between the driving hydromotors 21, 20 supplying same onthe other connection side through the pipeline represented by a solidline and through the distributors 2, 12 as an additional quantity to thedriving hydromotor 21. Thereby the left-hand driving hydromotor receivesmore oil and begins to rotate faster which matches the curvatureconditions when driving in a right-hand curve. The same oil quantity isremoved from the right-hand hydromotor 20 which corresponds to the lowerspeed of this wheel upon turning of vehicles to the right.

When driving in high gear the control pump belonging to thehydromotor-type distributor is short-circuited by the distributor 6. Inthe same way also the driving hydromotors 23 and 24 for the rear-axlewheels of the vehicle are short-circuited by distributors 9 or 10,respectively, so that these wheels are not driven in high gear.

The operation of the valve-type distributor 13 or 22, respectively,according to FIG. 3, the insertion of which into the hydraulic circuitof the hydrostatic drive arrangement for vehicles is shown in FIG. 2, isthe following: When one of the wheels of an axle runs onto slipperyground and, consequently, sideslides, the wheel rotates faster than thespeed corresponding to vehicle speed and curvature radius. As thedriving hydromotor of this wheel also rotates faster than the hydromotorof the wheel on the opposed side of the axle, there are differing oilflows through the connection points 16/19 and 18 at stake due tothrottling of the flows. The driving oil supplied to the valve-typedistributor 13 or 22 by the hydromotor-type distributor 3, 4, 5 (FIG. 2)enters the opening of the connection point 14/17 (FIG. 3) which isfitted to the common casing 29 and divided between the left-hand 86 andright-hand chamber 85, wherefrom it enters through the channel 30 or 31into chamber 48 or 51 and passes through grooves 74 or 75 made in thecylindrical head 56 or 57 of the movable shutter 58 or 59 and through anopening of the partition wall 54 or 55 into the chamber 49 or 52,respectively, which on its outer wall has the connection point 16/19 or15/ 18 for the connection of a supply pipeline to the left-handhydromotor 21 or 24 of the front or the rear axle and to the right-handdriving hydromotor or 23 of the front or rear axles of the vehicle. Atthe partition wall 54 through which protrudes the cylindrical head 56 ofthe movable shutter there is a pipe connection 71 on one side of thewall and a pipe con nection 70 on the other side of the wall, which areconnected to the first chamber of a piston servomotor. At the partitionwall 55 through which protrudes the cylindrical head 57 of the movableshutter there is a pipe connection 73 on one side of the wall and a pipeconnection 72 on the other side of the wall, which are connected to thesecond chamber of the piston servomotor. When driving straight ahead,equal driving-oil quantities flow through each movable shutter 58 and 59because both driving hydromotors, e.g. 20, 21 on the front axle, rotatewith the same speeds. With equal flows through the two movable shuttersthe differences of pressure of both sides of shutters in pipeconnections 71, 70 and 73, 72 are equal so that P11 P10 P13 1 12' Due tointerconnection of the pipe connections 71, 70 or 73, 72 withcompartments 119, 121 or 125, 123 the pressure differences of both sidesof pistons 114 or 115 will be equal, hence:

Pris Pr21 P125 'Prza- Thus the servomotor will stand still and therebyalso the control piston 98 of the four-way distributor which isconnected to the piston rod of the servomotor and held in its middleposition by the helicoidal pressure spring 108. In this position thefour-way distributor 33 blocks the inlet of the control oil through theconnection 47 and through the chambers 106 and 107 and the channel 39 or40 to which the chamber or 91 of the control throttle distributor 32 isconnected by the control pipeline 41 or 42 and the connection 44 or 45.The piston 82 of the distributor 32 in this case stands still in itsmiddle position due to the opposed actions of springs 94, 95. Thisfaciliates an unthrottled flow and a uniform distribution of the drivingoil between the connection points 16/19 and 15/ 18.

In the case when one of the wheels, e.g. the one driven by the drivinghydromotor 21 (FIG. 2), begins sidesliding because it happens to run upon mud, the flow of driving oil increases through the connection point16/19 of the distributor 13. Therefore the flow through the movableshutter 58 is greater than that through the movable shutter 59. Thus agreater pressure difference arises on the shutter 58 than on the shutter59 so that on pipe connections 71, 70 and 73, 72 the following ratio ofpressures prevails:

P11 "P10 Pm P12- Therefrom there result the following pressuredifferences in the servomotor 34 in the compartments 119, 121 on thesides of piston 114 and in the compartments 125, 123 on the sides ofpiston 115:

P119 "P121 P P123 when [(1 119 Pr2r) (Pr25 Prza)] F where F is theeffective surface area of pistons 114 and 115 and S is the force of thespring 108 of the distributor 33. The control piston 98 of thedistributor moves to the right. Thereby a connection is establishedbetween the control-oil connection 47 and the connection channel 39which by the control pipe 41 through the reversing valve 43 used forreversing drive is connected to chamber 90 of the control throttledistributor 32. In the formerly mentioned position of the control piston98 the connection channel 40 remains connected to the connection 46 ofthe pipelines for the control-oil tank. This connection is realizedthrough the chamber 107, the end chamber 104 and the connection channelbetween chamber 104 and the connection 46 and serves together with pipe42 leading through the reversing valve 43 as a relief pipeline for thedischarge of oil from chamber 91. In the position mentioned of thecontrol piston 98 of the four-way distributor 33 the oil flows throughconnection 47 into the middle chamber 103; through chamber 106, channel39 and control pipe 41 into chamber 90 of the control throttle valve 32,thereby pushing the piston 82 to the right. Consequently the taperedpiston part closes the distribution chamber 86 and reduces the flowthrough the channel 30 and the left-hand shutter 58 for such a timeuntil the flows through both shutters 58, 59 or through connectionpoints 16/19, 15/18 are balanced. Then the control piston 98 of thefour-way distributor and the piston 82 of the control throttledistributor return to their middle position.

Differing numbers of revolutions of two wheels of the same axle whendriving in a right-hand or left-hand curve are rendered possible byspring-loaded shutters 58, 59 which in the case of small differences ofspeeds and thus also of small differences of flows or pressures in thechamber 48, 49 or chamber 51, 52 move out of the middle position. Inthis way a larger cross-section of the groove 74 or 75 of thecylindrical head 56 or 57 of the movable shutter comes into zones ofpartition walls 54 or 55 faciliating a greater supply of driving oilthrough the connection point 16/19 or 15/18 and thereby to the drivinghydromotors 21, 24 or 20, 23 of the left-hand or right-hand wheelsaccording to a drive in a right-hand or lefthand curve. Due toinsufficient sensibility thereby the servomotor 34, the four-waydistributor 33 and the control throttle distributor 32 do not becomeeffective for throttling this greater flow to one of the drivinghydromotors of the wheel. These organs do not react before there arisesa greater difference of rotational speeds of wheels, e.g. at sideslidingof one wheel on mud. At transition of the vehicle from the curve instraight on drive, the spring 64 or 65 automatically returns thepertinent movable shutter 58 or 59 into their middle position, wherebyequal flows are again established through both shutters.

The operation of the hydromotor-type distributor 13' or 22 according toFIG. 4, the insertion of which into the hydraulic circuit of thehydrostatic drive arrangement for vehicles is shown in FIG. 2, is enoughclear from the description of its design so further discussion thereofis unnecessary.

The flow distributor 13" or 22" with feeler pumps for the distributionof the hydraulic medium between the driving hydromotors of the front andrear axles, respectively, according to FIG. 5, the insertion of whichinto the hydraulic circuit is shown in FIG. 2, operates as follows:

The main variable-flow driving pump (not shown in FIG. supplies by thepipeline through the connection point 14/17 driving oil to constant-flowhydromotor 204. The speed of said hydromotor only depends upon the oilquantity supplied by the pipe to connection point 14/ 17 (FIG. 2). Thehydromotor 204 propels the control pump 205, the control mechanism'ofwhich is linked to the steering mechanism of wheels of the vehicle sothat the magnitude and direction of deviation of the control mechanismof said pump depend upon the position of the steering gear of wheels ofthe vehicle. Besides, by the steering gear the direction of oil flowpropelled through control pipelines (drawn in FIG. 5 by a dotted line)by the control pump 205 can also be changed by the change of the senseof rotation of hydromotor 204, arising at a change of flow direction ofthe driving oil through the hydromotor 204. In this case the maindriving pump (not shown in FIG. 5) supplies driving oil through theconnection pipe 203 into the driving hydraulic circuit shown in FIG. 5by a thick solid, wherefrom the oil returns through the hydromotor and apipe connected to the connection point 14/ 17 again to the main drivingpump. The flow direction of the driving oil acts on the position of thepiston of the direction distributor 206. When the driving oil arrivesfrom the hydromotor 204 into the direction distributor 206, it pushesits piston into the end position and then flows through a by-passpipeline with a nonretum valve into a pipeline which splits into twobranches one of which is connected through a throttle distributor 207into the driving hydromotor 21 of the left-hand front wheel and theother branch into the driving hydromotor 20 of the right-hand frontwheel. In the middle position of the piston of the throttle distributorthe flow in both branches is not hindered in its way towards the drivinghydromotors. When the piston of the distributor 207 moves to the right,it throttles the flow in the branch leading to the driving hydromotor21, and when the piston moves to the left, it throttles the supply ofthe driving oil into the driving hydromotor 20. Behind the drivinghydromotors 21 and 20 both branches of the driving pipeline unite andreturn through the connection line 203 to the main driving pump. In thisway the driving hydromotors 20 and 21 are connected in parallel. Theshaft of the driving hydromotor 20 or 21 is linked to the shaft of thefeeler pump 21] or 210, respectively. When the constant-flow drivinghydromotors are used, the feeler pumps should be of the constant-flowtype, as well, when, however, variable-flow driving hydromotors areused, the feeler pumps can either be of the constant-flow or ofvariable-flow types.

As the shafts of pumps 210 and 211 rotate with the same speed as theshafts of driving hydromotors 21 and 20, the conditions in the pipebranches of the control circuit are similar to those in the drivingcircuit only at any lower pressure and with any smaller oil quantity.The pump 205 simulates differential operation and pumps oil from pipebranch 209 into pipe branch 208 or inversely, therewith balancing theoil flows which otherwise, when driving in a curve, would not be equaldue to differing speeds of the driving hydromotors 21 and 20 and feelerpumps 210 and 211 which are linked thereto. When the wheels driven bythe hydromotors 21 and 20 run correctly, i.e. so that neither of themslides, the pressures in the pipe branches 209 and 208 are equal. Thereexists no force acting upon the piston of the throttle distributor 7. Inthe case of sliding of any wheel, however, the pertinent feeler pump 210or 211 would press into the pipe branch 209 or 208 a larger oil quantitythan could be absorbed by the opposed feeler pump 211 or 210 in spite ofthe action of control pump 205. In this branch, consequently, anoverpressure arises which is trans mitted through the pipeline 212 or213 to one of the piston sides of the throttle distributor 207. Thispiston moves from it middle position and begins to throttle the oil flowfor the one driving hydromotor 21 or 20 the wheel of which sideslid. Dueto the pressure drop the torque of the driving hydromotor diminishes bysuch an amount that the wheel ceases sliding. In this moment thepressures in pipe branches 209 and 208 of the control circuit areequalized and the piston of the throttle distributor 207 begins toreturn into its middle position. As soon as the wheel again reachessolid ground, the pressures of both driving hydromotors are equalized,while otherwise the cycle described is repeated. Throttles 222, 223, 224and 225 are foreseen in order to switch off the control equipment whenthe vehicle or the machine attain such a speed which eliminates thedanger of wheel sliding due to the reduction of circumferential forces.The flow direction of control oil for flow correction in the two pipebranches 209, 208 and in the pipeline 212 is shown by arrows drawn alongthese pipes, whereby the reference marks have the following meanings:

N.O.D. forward, right-hand curve N.O.L. forward, left-hand curve V.O.D.backward, right-hand curve V.O.L. backward, left-hand curve In the caseone of the wheels begins to slide its feeler pump absorbs a larger oilquantity than is supplied to it by the feeler pump of the opposed wheel.In order to prevent a vacuum in this pump, it draws oil from the tank237 or 236 through pipe branches 226 or 227 or 228 or 229, respectively,which are equipped with non-retum valves.

When the piston of the throttle distributor 207 is out of its middleposition and the reason for sliding of a wheel eliminated, under theinfluence of a spring the piston returns to its middle position becausethe throttle 238 or 239 permits the return of oil from the distributor207 or from the control circuit into the tank.

The relief valves 232 or 233 have the task of eliminating the operationof the entire arrangement as soon as the vehicle reaches a sufficientspeed, thereby preventing an eventual operation of the throttledistributor 207 at high speeds and establishing an ideal parallelconnection of driving hydromotors when there is no danger ofwheel-sliding.

The tolerence of irregularities of running can be selected at will bythe dimensions of throttles 239, 238. When driving a vehicle one musthave in mind instantaneous changes of tire diameters due to shocks andvarying axle loadings. For permanent replenishment of control oil in theequipment a supply line 241 is provided having two nonretum valvesinserted into the pipe interconnecting the two pipe branches 208, 209 ofthe circuit.

The hydrostatic drive arrangement for vehicles according to theinvention has the advantage of an automatic adaptation ofcircumferential forces of any individual driven wheel of the vehiclewhen driving on a ground where hard soil with a goood adhesion of tireschanges to soft sections which by their low friction coefiicient presenta weak support for the circumferential force of the driving wheel. Thusany sliding of any individual wheel is excluded and an optimumutilization of the circumferential force of any individual driving wheelensured. This achievement is reflected by the great traction force ofthe vehicle, and it faciliates an optimum utilization of the drivingengine of the vehicle at low speeds and great traction forces whichcould not be attained with drives known until the present and which is aweighty problem at todays state of the art. A further advantage of thedrive arrangement according to the invention is a lower weight of thevehicle and less driving power of the engine needed, which factors allhave an essential influence on the price of the vehicle. Beside theproperties mentioned above the vehicle according to the invention hasthe advantage that the individual wheels at the adaptation to frictionconditions at the same time also automatically adapt to curvatureconditions. Thus the wheels most favorably utilize their circumferentialforces on grounds having nonuniform friction coefficients when drivingin curves without sliding because of differing speeds required for suchdriving. Thereby also the wear of tires is minimalized.

It is, however, still within the frame of the invention if a valve-typedistributor or a distributor with feeler pumps is used for flowdistribution of the hydraulic medium between the groups of drivinghydromotors of the front and rear axles of the vehicle.

We claim:

1. A hydrostatic drive for a vehicle having front and rear wheels, saiddrive comprising:

respective hydraulic-motor means operatively connected to said frontwheels and to said rear wheels for respectively driving same, each ofsaid hydraulic-motor means including respective driving hydromotorsconnected to the corresponding right and left wheels, respectively;

at least one main hydraulic pump connected in hydraulic circuit withsaid hydraulic-motor means for hydraulically energizing same; hydromotorflow distributor connected in said circuit between said hydraulic-motormeans and said main pump for the distribution of a hydraulic mediumtherebetween to adapt the rotary speeds of the individual wheels to roadcurvature encountered by said vehicle; and

a respective further flow distributor including valve means connectedbetween the drive hydromotors of each pair of right and left wheels, andbetween the respective hydromotors and the corresponding hydromotor flowdistributor for individually adapting the circumferential force appliedto each wheel to the respective road-wheel friction, said circuitincluding a respective primary hydraulic connection between saidhydromotor flow distributor and each of said further flow distributorsfor supplying fluid to the latter, and a respective secondary hydraulicconnection between each of said further flow distributors and thedriving hydromotors of the corresponding pair of right and left wheels,said hydromotor flow distributor including:

a respective constant-displacement hydraulic motor having an inputconnected to said main pump and an output communicating with arespective one of said primary connections;

a hydraulic control pump having its opposite sides connected across theoutputs of said constant-displacement hydraulic motors, saidconstant-displacement 50 hydraulic motors and said control pump havingrespective shafts; and

means mechanically connecting said shafts for joint operation thereof ina fixed predetermined relationship.

2. The hydrostatic drive defined in claim 1 for a vehicle having alow-speed, high-torque operating mode wherein the outlets of saiddriving hydromotors are connected in parallel through a valve-typedistributor system.

3. The hydrostatic drive defined in claim 1 wherein said 60 vehicle hasan intermediate-speed, intermediate-torque operating condition, furthercomprising valve means shunted across said control pump in saidoperating condition.

4. The hydrostatic drive defined in claim 1 for a vehicle having alow-speed, high-torque operating mode, further compris- 65 ing afour-way distributor connected to one side of said constant-displacementhydraulic motors and further valves distributors connecting the otherside of said constant-displacement hydraulic motors to said drivingmotors of said front and rear wheels in parallel.

5. The hydrostatic drive defined in claim 4 wherein said vehicle has asteering mechanism, said drive further comprising a control valveconnected across said control pump for selectively shunting same inresponse to operation of said steering mechanism.

6. The hydrostatic drive defined in claim ll wherein said vehicle has anintermediate-speed, intermediate-torque condition, said drive furthercomprising a four-way distributor connected to said further flowdistributor for operating said hydromotors in parallel.

7. The hydrostatic drive defined in claim 6, further comprising valvemeans for shunting the driving hydromotors of one of said pairs ofwheels in said intermediate-speed, intermediate-torque condition of saidvehicle.

8. The hydrostatic drive defined in claim 1 wherein said vehicle has ahigh-speed, low-torque condition, further comprising a four-waydistributor connected to said hydromotor flow distributor, the pressureside of said main pump being connected to one side of one of saidconstant-displacement hydraulic motors via said four-way distributor insaid condition, said drive further comprising another distributorconnecting said main pump with one side of one of said drivinghydromotors and the other side of said driving hydromotor in seriesthrough the other driving hydromotor of a respective pair of wheels, andmeans connecting the discharge side of the other driving hydromotor withthe other of said constant-displacement hydraulic motors, said controlpump being shunted in said condition.

9. The hydrostatic drive defined in claim 8, further comprising meansfor shunting the hydromotors of the other pair of wheels in saidcondition.

10. A hydrostatic drive for a vehicle having front and rear wheels, saiddrive comprising:

respective hydraulic-motor means operatively connected to said frontwheels and to said rear wheels for respectively driving same, each ofsaid hydraulic-motor means including respective driving hydromotorsconnected to the corresponding right and left wheels, respectively;

at least one main hydraulic pump connected in hydraulic circuit withsaid hydraulic-motor means for hydraulically energizing same; hydromotorflow distributor connected in said circuit between said hydraulic-motormeans and said main pump for the distribution of a hydraulic mediumtherebetween to adapt the rotary speeds of the individual wheels to roadcurvature encountered by said vehicle; and a respective further flowdistributor including valve means connected between the drivehydromotors of each pair of right and left wheels, and between therespective hydromotors and the corresponding hydromotor flow distributorfor individually adapting the circumferential force applied to eachwheel to the respective road-wheel friction, said circuit including arespective primary hydraulic connection between said hydromotor flowdistributor and each of said further flow distributors for supplyingfluid to the latter, and a respective secondary hydraulic connectionbetween each of said further flow distributors and the drivinghydromotors of the corresponding pair of right and left wheels, each ofsaid further flow distributors and the associated valve means comprisinga feeler assembly sensing flow-pressure differences in the hydraulicmedium at the hydromotors of the respective pair of wheels caused byslippage thereof for controlling the hydraulic fluid supply to saiddrive hydromotors, said feeler assembly comprising:

a casing;

throttle-valve means in said casing and including means defining a pairof valve seats communicating with the respective primary hydraulicconnection,

a pair of throttle-valve chambers respectively communicating with saidseats, and

a throttle-valve member shiftable for throttling the flow of hydraulicmedium from each of said thrott1e-valve seats to the respectivethrottle-valve chambers in reciprocal senses; said chamberscommunicating with the respective secondary connections;

a four-way spool-type distributor valve having a pair of outputscommunicating with said throttle valve means and effective to bias saidthrottle-valve member in opposite directions, and a pair of inputsconnected to a source of a control fluid;

reversing-valve means between said outputs of said distributing valveand said throttle-valve means; and

a piston-type servomotor mounted on said distributing valve andconnected thereto while communicating with said chambers for controllingsaid spool-type distributing valve.

11. The hydrostatic drive defined in claim 10 wherein saidthrottle-valve means includes a housing defining a valve bore fonnedwith said seats and said chambers and slidably receiving saidthrottle-valve member, a space along said bore communicating in commonwith said seats and a channel between a respective primary connectionand said space, said throttle valve member having a pair of valve headstapered in the direction of the respective seats and cooperatingtherewith, and respective small-diameter portions on the ends of saidmember, said throttle-valve means further comprising spring meansbearing on said member in opposite directions for centering samerelative to said seats, said spring means including a coil springsurrounding each of said ends and bearing outwardly upon said casing andrespective supporting plates seated against said springs and bearingupon said heads around said ends.

12. The hydrostatic drive defined in claim 10 wherein said servomotorincludes a piston operatively connected to the spool of said distributorvalve and formed with a pair of spaced-apart piston members, aservomotor housing surrounding said piston defining a pair of workingchambers each slidably receiving one of said piston members andsubdivided thereby into a pair of oppositely effective workingcompartments, and respective duct means connecting each pair of saidworking compartments to a respective one of said throttlevalve chambersfor displacement of said piston in response to pressure differentialcreated in the hydraulic medium of said throttle-valve chambers.

13. The hydrostatic drive defined in claim 10 wherein said spool-typedistributing valve comprises a control piston having a central spool anda pair of outer spools spaced from said central spool;

a valve housing slidably receiving said control piston and formed with acentral space communicating with a source of a hydraulic medium and apair of further spaces respectively connected with said reversing valveand communicating selectively with said central space upon displacementof said central spool in either direction from an intermediate positionof the control piston, said valve housing being further provided with apair of outer spaces communicating with a reservoir of the hydraulicmedium and with each of said further spaces respectively but blockableby said outer spools upon displacement of said control piston; and

spring means acting upon said control piston for biasing same into saidintermediate position upon displacement of said control piston by saidservomotor.

14. The hydrostatic drive defined in claim 13 wherein said spring meansincludes a pair of shoulders fonned on said control piston in axiallyspaced relation, a pair of support plates slidably mounted on saidcontrol piston between said shoulders and engageable with opposite wallsof said valve housing,

and a coil spring surrounding said control piston and seated againstsaid plates, said valve housing defining an abutment engageable withsaid control piston to limit the displacement thereof in one direction.

15. The hydrostatic drive defined in claim 10 wherein said feelerassembly further comprises:

means on said casing defining a pair of control compartmentsrespectively connected with said throttle-valve chambers and formedinternally with respective panitions, said compartments each beingconnected on one side of a respective partition to the respectivechamber and on the other side of the partitions to a respective one ofsaid seconda hydraulic connections; means hydraulical y connecting theopposite sides of each of said partitions to said servomotor for biasingsame in accordance with the pressure differential across saidpartitions;

respective throttle heads traversing said partitions for controlling thepressure differential developed thereacross, each of said heads beingformed with an upstanding stem; and

spring means cooperating with said stems for biasing said heads intointermediate positions relative to said partitlons.

16. The hydrostatic drive defined in claim 15 wherein said servomotorcomprises a piston rod connected with said spool and formed with a pairof spaced-apart piston members, and cylinder means surrounding saidpiston members and defining a pair of working chambers subdivided bysaid piston members into respective pairs of working compartments, saidfeeler means including first duct means communicating with said controlcompartments along the side of the partition connected with theassociated throttle-valve chamber and communicating with the workingcompartments of said servomotor acting upon said piston members inopposite directions, and second duct means connected to said controlcompartments on the sides of said partitions remote from saidthrottlevalve chambers and connected to the remaining workingcompartments of said servomotor.

17. The hydrostatic drive defined in claim 15 wherein each of said headsis generally cylindrical and is formed with at least one longitudinalslot of a cross section increasing continuously outwardly from arelative small cross section centrally of the head.

18. The hydrostatic drive defined in claim 15 wherein each of said stemsis provided with a pair of axially spaced shoulders and said springmeans includes a coil spring surrounding each stem between saidshoulders, and a pair of supporting plates forming seats for said coilspring and urged thereby against said shoulders, said casing beingprovided with further compartments receiving said spring means andhaving walls engageable with said plates while permitting displacementof said stems, the plate between said further compartment and saidcontrol compartment being provided with a bore for equalization of thepressure between said further compartment and the respective controlcompartment, said casing being formed with blind bores slidablyreceiving said stems remote from said heads, and respective passagesconnecting said blind bores and said further compartments forequalization of the fluid pressure therebetween.

1. A hydrostatic drive for a vehicle having front and rear wheels, saiddrive comprising: respective hydraulic-motor means operatively connectedto said front wheels and to said rear wheels for respectively drivingsame, each of said hydraulic-motor means including respective drivinghydromotors connected to the corresponding right and left wheels,respectively; at least one main hydraulic pump connected in hydrauliccircuit with said hydraulic-motor means for hydraulically energizingsame; a hydromotor flow distributor connected in said circuit betweensaid hydraulic-motor means and said main pump for the distribution of ahydraulic medium therebetween to adapt the rotary speeds of theindividual wheels to road curvature encountered by said vehicle; and arespective further flow distributor including valve means connectedbetween the drive hydromotors of each pair of right and left wheels, andbetween the respective hydromotors and the corresponding hydromotor flowdistributor for individually adapting the circumferential force appliedto each wheel to the respective road-wheel friction, said circuitincluding a respective primary hydraulic connection between saidhydromotor flow distributor and each of said further flow distributorsfor supplying fluid to the latter, and a respective secondary hydraulicconnection between each of said further flow distributors and thedriving hydromotors of the corresponding pair of right and left wheels,said hydromotor flow distributor including: a respectiveconstant-displacement hydraulic motor having an input connected to saidmain pump and an output communicating with a respective one of saidprimary connections; a hydraulic control pump having its opposite sidesconnected across the outputs of said constant-displacement hydraulicmotors, said constant-displacement hydraulic motors and said controlpump having respective shafts; and means mechanically connecting saidshafts for joint operation thereof in a fixed predeterminedrelationship.
 2. The hydrostatic drive defined in claim 1 for a vehiclehaving a low-speed, high-torque operating mode wherein the outlets ofsaid driving hydromotors are connected in parallel through a valve-typedistributor system.
 3. The hydrostatic drive defined in claim 1 whereinsaid vehicle has an intermediate-speed, intermediate-torque operatingcondition, further comprising valve means shunted across said controlpump in said operating condition.
 4. The hydrostatic drive defined inclaim 1 for a vehicle having a low-speed, high-torque operating mode,further comprising a four-way distributor connected to one side of saidconstant-displacement hydraulic motors and further valves distributorsconnecting the other side of said constant-displacement hydraulic motorsto said driving motors of said front and rear wheels in parallel.
 5. Thehydrostatic drive defined in claim 4 wherein said vehicle has a steeringmechanism, said drive further comprising a control valve connectedacross said control pump for selectively shunting same in response tooperation of said steering mechanism.
 6. The hydrostatic drive definedin claim 1 wherein said vehicle has an intermediate-speed,intermediate-torque condition, said drive further comprising a four-waydistributor connected to said further flow distributor for operatingsaid hydromotors in parallel.
 7. The hydrostatic drive defined in claim6, further comprising valve means for shunting the driving hydromotorsof one of said pairs of wheels in said intermediate-speed,intermediate-torque condition of said vehicle.
 8. The hydrostatic drivedefined in claim 1 wherein said vehicle has a high-speed, low-torquecondition, further comprising a four-way distributor connected to saidhydromotor flow distributor, the pressure side of said main pump beingconnected to one side of one of said constant-displacement hydraulicmotors via said four-way distributor in said condition, said drivefurther comprising another distributor connecting said main pump withone side of one of said driving hydromotors and the other side of saiddriving hydromotor in series through the other driving hydromotor of arespective pair of wheels, and means connecting the discharge side ofthe other driving hydromotor with the other of saidconstant-displacement hydraulic motors, said control pump being shuntedin said condition.
 9. The hydrostatic drive defined in claim 8, furthercomprising means for shunting the hydromotors of the other pair ofwheels in said condition.
 10. A hydrostatic drive for a vehicle havingfront and rear wheels, said drive comprising: respective hydraulic-motormeans operatively connected to said front wheels and to said rear wheelsfor respectively driving same, each of said hydraulic-motor meansincluding respective driving hydromotors connected to the correspondingright and left wheels, respectively; at least one main hydraulic pumpconnected in hydraulic circuit with said hydraulic-motor means forhydraulically energizing same; a hydromotor flow distributor connectedin said circuit between said hydraulic-motor means and said main pumpfor the distribution of a hydraulic medium therebetween to adapt therotary speeds of the individual wheels to road curvature encountered bysaid vehicle; and a respective further flow distributor including valvemeans connected between the drive hydromotors of each pair of right andleft wheels, and between the respective hydromotors and thecorresponding hydromotor flow distributor for individually adapting thecircumferential force applied to each wheel to the respective road-wheelfriction, said circuit including a respective primary hydraulicconnection between said hydromotor flow distributor and each of saidfurther flow distributors for supplying fluid to the latter, and arespective secondary hydraulic connection between each of said furtherflow distributors and the driving hydromotors of the corresponding pairof right and left wheels, each of said further flow distributors and theassociated valve means comprising a feeler assembly sensingflow-pressure differences in the hydraulic medium at the hydromotors ofthe respective pair of wheels caused by slippage thereof for controllingthe hydraulic fluid supply to said drive hydromotors, said feelerassembly comprising: a casinG; throttle-valve means in said casing andincluding means defining a pair of valve seats communicating with therespective primary hydraulic connection, a pair of throttle-valvechambers respectively communicating with said seats, and athrottle-valve member shiftable for throttling the flow of hydraulicmedium from each of said throttle-valve seats to the respectivethrottle-valve chambers in reciprocal senses; said chamberscommunicating with the respective secondary connections; a four-wayspool-type distributor valve having a pair of outputs communicating withsaid throttle valve means and effective to bias said throttle-valvemember in opposite directions, and a pair of inputs connected to asource of a control fluid; reversing-valve means between said outputs ofsaid distributing valve and said throttle-valve means; and a piston-typeservomotor mounted on said distributing valve and connected theretowhile communicating with said chambers for controlling said spool-typedistributing valve.
 11. The hydrostatic drive defined in claim 10wherein said throttle-valve means includes a housing defining a valvebore formed with said seats and said chambers and slidably receivingsaid throttle-valve member, a space along said bore communicating incommon with said seats and a channel between a respective primaryconnection and said space, said throttle valve member having a pair ofvalve heads tapered in the direction of the respective seats andcooperating therewith, and respective small-diameter portions on theends of said member, said throttle-valve means further comprising springmeans bearing on said member in opposite directions for centering samerelative to said seats, said spring means including a coil springsurrounding each of said ends and bearing outwardly upon said casing andrespective supporting plates seated against said springs and bearingupon said heads around said ends.
 12. The hydrostatic drive defined inclaim 10 wherein said servomotor includes a piston operatively connectedto the spool of said distributor valve and formed with a pair ofspaced-apart piston members, a servomotor housing surrounding saidpiston defining a pair of working chambers each slidably receiving oneof said piston members and subdivided thereby into a pair of oppositelyeffective working compartments, and respective duct means connectingeach pair of said working compartments to a respective one of saidthrottle-valve chambers for displacement of said piston in response topressure differential created in the hydraulic medium of saidthrottle-valve chambers.
 13. The hydrostatic drive defined in claim 10wherein said spool-type distributing valve comprises a control pistonhaving a central spool and a pair of outer spools spaced from saidcentral spool; a valve housing slidably receiving said control pistonand formed with a central space communicating with a source of ahydraulic medium and a pair of further spaces respectively connectedwith said reversing valve and communicating selectively with saidcentral space upon displacement of said central spool in eitherdirection from an intermediate position of the control piston, saidvalve housing being further provided with a pair of outer spacescommunicating with a reservoir of the hydraulic medium and with each ofsaid further spaces respectively but blockable by said outer spools upondisplacement of said control piston; and spring means acting upon saidcontrol piston for biasing same into said intermediate position upondisplacement of said control piston by said servomotor.
 14. Thehydrostatic drive defined in claim 13 wherein said spring means includesa pair of shoulders formed on said control piston in axially spacedrelation, a pair of support plates slidably mounted on said controlpiston between said shoulders and engageable with opposite walls of saidvalve housing, and a coil spring surrounding said control piston andseated against said plates, said valve housing defining an abutmentengageable with said control piston to limit the displacement thereof inone direction.
 15. The hydrostatic drive defined in claim 10 whereinsaid feeler assembly further comprises: means on said casing defining apair of control compartments respectively connected with saidthrottle-valve chambers and formed internally with respectivepartitions, said compartments each being connected on one side of arespective partition to the respective chamber and on the other side ofthe partitions to a respective one of said secondary hydraulicconnections; means hydraulically connecting the opposite sides of eachof said partitions to said servomotor for biasing same in accordancewith the pressure differential across said partitions; respectivethrottle heads traversing said partitions for controlling the pressuredifferential developed thereacross, each of said heads being formed withan upstanding stem; and spring means cooperating with said stems forbiasing said heads into intermediate positions relative to saidpartitions.
 16. The hydrostatic drive defined in claim 15 wherein saidservomotor comprises a piston rod connected with said spool and formedwith a pair of spaced-apart piston members, and cylinder meanssurrounding said piston members and defining a pair of working chamberssubdivided by said piston members into respective pairs of workingcompartments, said feeler means including first duct means communicatingwith said control compartments along the side of the partition connectedwith the associated throttle-valve chamber and communicating with theworking compartments of said servomotor acting upon said piston membersin opposite directions, and second duct means connected to said controlcompartments on the sides of said partitions remote from saidthrottle-valve chambers and connected to the remaining workingcompartments of said servomotor.
 17. The hydrostatic drive defined inclaim 15 wherein each of said heads is generally cylindrical and isformed with at least one longitudinal slot of a cross section increasingcontinuously outwardly from a relative small cross section centrally ofthe head.
 18. The hydrostatic drive defined in claim 15 wherein each ofsaid stems is provided with a pair of axially spaced shoulders and saidspring means includes a coil spring surrounding each stem between saidshoulders, and a pair of supporting plates forming seats for said coilspring and urged thereby against said shoulders, said casing beingprovided with further compartments receiving said spring means andhaving walls engageable with said plates while permitting displacementof said stems, the plate between said further compartment and saidcontrol compartment being provided with a bore for equalization of thepressure between said further compartment and the respective controlcompartment, said casing being formed with blind bores slidablyreceiving said stems remote from said heads, and respective passagesconnecting said blind bores and said further compartments forequalization of the fluid pressure therebetween.